The present invention relates a stretched antistatic laminate polyester film. More particularly, the present invention relates to a stretched antistatic laminate film prepared by coating a polymer having pyrrolidium rings to at least one surface of a polyester film and then stretching the resultant film, a magnetic recording medium having a magnetic layer on the stretched antistatic laminate film, a film having a silicon resin layer on the stretched antistatic laminate film, recording material for a thermal transfer printing having the stretched antistatic laminate film, as well as a method of manufacturing a film having the stretched antistatic laminate film.
Biaxially stretched polyester films have generally been used as a film having excellent properties but they have a fault of being easily charged.
As a method of preventing static charges, there are a method of kneading an anionic compound such as an organic sulfonate and organic phosphate, a method of vacuum-evaporating a metal compound, a method of coating an anionic compound, cationic compound or so-called electroconductive particles, etc. The method of kneading the anionic compound can be conducted at a reduced cost but it involves problems such as the limit for the antistatic effect, as well as deterioration in the adhesion between the film and the laminated layer due to blooming, lacking in water proofness and transferring the compound since the compound usable herein is a low molecular weight compound. The method of vacuum-evaporating the metal compound can provide excellent antistatic effect and the application use for transparent electroconductive films of the resultant films has been increased in recent years. However, since the production cost thereof is high, it is unfavorable to use the method for usual antistatic films although suitable to particular application uses. The method of coating the electroconductive carbon or electroconductive metal particles has relatively satisfactory antistatic effect and a merit capable of producing films at a relatively reduced cost, but it has a fault that the transparency of the films become worse.
In view of the above, a method of coating an anionic compound or cationic compound as the antistatic agent has generally been employed as the antistatic method of biaxially stretched polyester films.
For the method of manufacturing a biaxially stretched polyester film having a coating layer, there is known a coating and stretching method of applying a coating solution to a film, stretching the thus obtained film and subjecting to the thus stretched film heat-treatment (in-line coating method). As compared with the method of forming a coating layer by applying a coating solution to a biaxially stretched polyester film, since the film-formation and the coating can be practiced simultaneously in this method, wide film products can be obtained at a relatively reduced cost as well as the resultant films have good adhesion between the coating layer and the polyester film as the substrate, the thickness of the coating layer can be thinned and the surface property of the coating layer is excellent.
However, in the case producing an antistatic polyester film by the in-line coating method, since the antistatic agent is thermally instable, it results in volatilization or heat decomposition during stretching step and heat-treatment step, thereby sometime failing to obtain an expected antistatic effect in the case where the coating step and stretching step are practiced under usual conditions.
On the other hand, under the state where the conditions for the heat-treatment such as processing temperature or staying time of the film are moderated, although the volatilization or heat decomposition of the antistatic agent can be suppressed and as a result, an antistatic effect is exhibited, the resultant films have only insufficient mechanical strength, insufficient dimensional stability, etc.
There are some cases where such films can not always be applied, particularly, to magnetic recording material and recording material for heat sensitive transfer printing, or where a silicon resin lamination can not be carried out on such films.
As a result of the present inventors' earnest study for solving the foregoing problems, it has been found that a laminate film excellent in the antistatic effect and heat resistance can be manufactured easily with no particular attentions in the steps of coating, stretching and subjecting to heat-treatment in the in-line coating method, by using a coating solution containing a polymer having pyrrolidium rings in the main molecular chain as a coating solution which is to be coated at least on one surface of a polyester film, and the present invention has been accomplished based on such a finding.